JP2012148961A - Method of manufacturing vitreous silica crucible - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a vitreous silica crucible having a suitably controlled inner surface property (property of the crucible inner surface).SOLUTION: The present invention provides a method of manufacturing a vitreous silica crucible by heating and fusing a silica powder layer 11 in a rotating mold 10 by arc discharge generated by a plurality of carbon electrodes 13, including: a preparation step of determining optimal fusing temperatures during heating and fusing the silica powder layer 11 at plural points of the silica powder layer; a temperature measuring step of measuring actual temperatures during heating and fusing the silica powder layer at the plural points; a temperature controlling step of controlling the actual temperatures at the plural points so that the actual temperatures matches the optimal fusing temperatures.

Description

  The present invention relates to a method for producing a silica glass crucible preferably used for pulling a silicon single crystal.

  A Czochralski method (CZ method) using a silica glass crucible (hereinafter sometimes simply referred to as a crucible) is employed for the production of a silicon single crystal. In the CZ method, a silicon melt obtained by melting a silicon polycrystalline raw material is stored in a silica glass crucible. Then, the silicon single crystal is grown using the seed crystal as a nucleus by immersing the silicon single crystal in a silicon melt and gradually pulling it up.

The silica glass crucible used in such a CZ method is a so-called rotary mold method in which silica powder is supplied into a rotary mold to form a silica powder layer, and this silica powder layer is heated and melted by arc discharge of a carbon electrode. It is manufactured. In the rotary molding method, the arc-melted portion has a high temperature exceeding 2000 ° C.
Further, the silica glass crucible produced in this way has a two-layer structure consisting of an outer layer containing many bubbles and a transparent inner layer. Here, the surface of the inner layer (the characteristics of the inner surface that is in contact with the silicon melt when the single crystal is pulled is influenced by the characteristics of the silicon single crystal to be pulled, and the final silicon wafer yield is also affected. It has been known.

  Specifically, for example, when pulling up a single crystal using a silica glass crucible, a wave is generated on the surface of the silicon melt, making it difficult to seed the seed crystal by proper immersion. In this case, there has been a problem that the silicon single crystal cannot be pulled up or the single crystallization is hindered. This phenomenon is called molten metal vibration, and it is more likely to occur with the recent increase in the diameter of silicon single crystals. Moreover, it is known that such a molten metal surface vibration phenomenon is related to the state of the inner surface of the silica glass crucible. Against this background, for example, it is known to take measures as described in Patent Document 1.

In addition, as the diameter of a silicon single crystal needs to be increased in response to a wafer having a diameter of 300 mm or more and a diameter of about 450 mm, the pulling operation of the single crystal becomes longer, and the inner surface of the crucible is exposed to a silicon melt at 1400 ° C. or higher. It has come into contact for a long time. For this reason, the following problems have become apparent.
That is, when the pulling operation becomes longer, the time for the inner surface of the crucible to come into contact with the silicon melt also becomes longer. As a result, the inner surface of the crucible reacts with the silicon melt and crystallization occurs in the surface position of the inner surface of the crucible or in a shallow layer from the surface, and brown cristobalite may appear in a ring shape. Hereinafter, this ring-shaped material is referred to as a brown ring. Inside this brown ring, there is no cristobalite layer, or even if it is very thin layer, but with the passage of time, the brown ring expands its area and continues to grow while fusing with each other. The part is eroded and becomes an irregular glass elution surface.
When a minute glass piece falls off from such a glass elution surface, dislocation is likely to occur in the silicon single crystal, which hinders the yield (yield) of pulling the single crystal. In particular, in order to grow a silicon single crystal for producing a large-diameter wafer having a diameter of 300 mm or more, it is necessary to carry out the operation of the CZ method for over 100 hours, and the appearance of the glass elution surface becomes remarkable.

  Such a brown ring is considered to be generated with a fine flaw on the glass surface, a crystalline residue which is an unmelted raw material powder, defects in the glass structure, and the like as nuclei. Therefore, in order to reduce the number of brown rings, the state of the inner surface of the crucible is kept good, or in order to eliminate crystalline residual components, the time for melting the raw material powder in the crucible manufacturing process is increased to a higher temperature and longer time. As disclosed in Patent Documents 2 and 3, it is conceivable to use an amorphous synthetic powder as a raw material powder for forming the inner surface.

JP 2002-154894 A Japanese Patent No. 2811290 Japanese Patent No. 2933404

  However, a technique for producing a silica glass crucible whose inner surface state is appropriately controlled so that a silicon single crystal of good quality can be produced stably with high productivity has not been established.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the manufacturing method of the silica glass crucible in which the crucible characteristics, such as an inner surface state (crucible inner surface characteristic), were controlled appropriately.

  As a result of intensive studies on a method for obtaining a silica glass crucible in which the state of the inner surface and the like is appropriately controlled, such a crucible is heated and melted by arc discharge at a plurality of portions of the silica powder layer. By pre-determining the optimum melting temperature in advance, the silica powder layer is heated and melted while controlling these actual temperatures so that the actual temperatures (measured temperatures) at these multiple locations become the optimum melting temperatures, respectively. Found that it can be manufactured.

The method for producing a silica glass crucible of the present invention is a method for producing a silica glass crucible by heating and melting a silica powder layer by arc discharge using a plurality of carbon electrodes in a rotating mold,
For a plurality of locations where the height position of the silica powder layer is different, a preliminary step for obtaining in advance an optimum melting temperature at the time of heating and melting,
A temperature measuring step for measuring an actual temperature at the time of heating and melting at the plurality of locations;
A temperature control step of controlling the actual temperatures at the plurality of locations so as to achieve the optimum melting temperature.
The optimum melting temperature and the actual temperature are preferably the temperatures of the inner surfaces of the plurality of locations.
It is preferable to obtain the optimum melting temperature over time and control the actual temperature over time.
It is preferable that at least one of the plurality of locations is a location corresponding to a corner portion of the silica glass crucible.

  According to the present invention, with respect to the silica powder layer in a molten state, each actual temperature at a plurality of locations can be controlled to each optimum melting temperature in real time, and therefore, the molten state of the silica powder layer can be appropriately controlled. . As a result, a silica glass crucible in which the crucible characteristics such as the state of the inner surface are appropriately controlled can be manufactured.

In the present invention, the silica powder layer is heated and melted while rotating about the rotation axis of the mold. The “plural places” actually correspond to concentric “plural circumferential portions” having different height positions.
As will be described later, when obtaining the optimum melting temperature or measuring the actual temperature during heating and melting, a radiation thermometer that detects the radiant energy from the object to be measured and measures the temperature is used as the temperature measuring unit. Preferably used. When the radiation thermometer is fixed and the temperature at multiple locations of the rotating silica powder layer is measured, the temperature is naturally measured at the circumference, not at one spot. .

The optimum melting temperature is a temperature obtained empirically from temperature data when a crucible having good crucible characteristics capable of stably producing a good quality silicon single crystal with high productivity, or The preferred temperature is obtained by a computational method such as simulation.
The crucible characteristics include, for example, the vitrification state on the inner surface of the crucible, the bubble distribution and the bubble size in the thickness direction of the crucible, the OH group content, the impurity distribution, the surface irregularities, and the height of these crucibles. The distribution state is a factor that affects the characteristics of the silicon single crystal pulled by the quartz glass crucible.

  The silica glass crucible is an important member that determines the yield and quality of a silicon single crystal as the only member that comes into contact with the silicon melt. Depending on the bubble distribution and bubble size in the crucible thickness direction, when the silicon single crystal is pulled up, the bubble may burst and glass pieces may be mixed into the silicon melt, resulting in polycrystallization when attached to the silicon single crystal ingot. There is. Depending on the content of OH groups, the silica glass crucible is likely to crystallize and generate cristobalite, and the cristobalite peeled from the silica glass crucible may adhere to the silicon single crystal edge to polycrystallize the silicon single crystal. is there. Moreover, there is a possibility that silica is deformed due to low viscosity. In the presence of impurities, the impurities promote the formation of spotted cristobalite on the inner surface of the silica glass crucible during the crystal pulling process. The cristobalite thus formed separates from the crucible and falls into the silicon melt, thereby reducing the single crystallization rate of the single crystal to be pulled up.

  In particular, in a large-diameter crucible of 23 inches (58.4 cm) to 40 inches (116 cm), unevenness occurs in the inner surface temperature during melting, and as a result, in-plane distribution occurs in the state of the inner surface of the crucible. there were. According to the present invention, since the actual temperature at a plurality of locations can be controlled so as to reach the optimum melting temperature, the occurrence of such temperature unevenness is prevented, and a silica glass crucible having uniform inner surface characteristics in the circumferential direction is manufactured. It becomes possible to do.

  In the present invention, the state of the inner surface of the crucible that has a great influence on the characteristics of the silicon single crystal to be produced is particularly preferably controlled when the optimum melting temperature and the actual temperature are the temperatures of the inner surface at the plurality of locations. it can.

  In the present invention, in the preliminary step, the optimum melting temperature is obtained over time, and in the temperature control step, the actual temperature is controlled over time, so that the crucible such as the state of the inner surface is more reliably obtained. A silica glass crucible with appropriately controlled properties can be produced. The optimum melting temperature may be obtained at an important time, and temperature control may be performed at that time. Even in this case, the effect of the present invention can be obtained.

In the present invention, when one of the plurality of locations is a location corresponding to a corner portion of the silica glass crucible, the melting state of the silica powder layer can be controlled more precisely in the production of the silica glass crucible. .
The crucible is divided into three zones: a bottom part, a wall part, and a corner part. The corner part is located between, for example, a cylindrical wall part and a bottom part having a constant radius of curvature. It means the part to connect. In other words, the radius of curvature at the bottom of the wall begins to change from the center of the bottom toward the upper end of the opening along the inner surface of the crucible (infinite in the case of a cylindrical shape). The part is the corner.

In the radial direction from the center of the bottom of the silica powder layer to the upper end of the opening of the silica powder layer, the present inventors, as shown in FIG. 3, position B, position BR, position R, position RW Temperature measurement was performed on the six inner surfaces at positions W1 and W2.
Here, the position B is the center (on the rotation axis) of the bottom of the molded body. The position B-R is near the middle between the boundary between the bottom part and the corner part and the position B. The position R is a position near the boundary with the bottom portion in the corner portion. The position RW is a position near the boundary with the wall portion in the corner portion. The position W1 is near the middle between the boundary between the corner portion and the wall portion and the upper end of the opening. The position W2 is near the upper end of the opening.
Note that the vicinity of the middle between the position X and the position Y means a length range in which the ratio with respect to the distance XY is ± 5% from the middle position between the position X and the position Y. As a result, the measured temperature varied and the standard deviation was large at position RW and position R as shown in FIG.

  From this result, it is possible to control the melting state of the silica powder layer more precisely by calculating the optimum melting temperature for the corner and controlling the actual temperature so that this part becomes the optimum melting temperature. It becomes.

  At the corner, especially near the boundary with the wall of the corner, the molten glass tends to sag by gravity from the wall during melting, and the molten glass tends to approach from the bottom by centrifugal force due to the rotation of the mold. The thickness dimension tends to be larger than the set value. Therefore, the thickness of the crucible is controlled by obtaining the optimum melting temperature in advance for the corner portion, particularly the position near the boundary with the wall portion, and controlling the actual temperature of the portion to be the optimum melting temperature. It becomes possible.

  In the present invention, the optimum melting temperature is obtained at a plurality of locations, that is, at two or more locations, and the actual temperature is controlled. As the number of target locations increases, the accuracy improves, but the effort and cost increase. Therefore, the number of target locations is determined by a balance between accuracy, labor, and cost.

It is a model front view which shows one Embodiment of a silica glass crucible manufacturing apparatus. It is the model top view (a) which shows the carbon electrode which the silica glass crucible manufacturing apparatus of FIG. 1 comprises, and a model side view (b). It is a schematic diagram which shows the temperature measurement position of a silica powder layer. It is a graph which shows the dispersion | variation in the temperature by the temperature measurement position of a silica powder layer, and is a graph (a) which shows a standard deviation, and a graph (b) which shows the measured temperature. It is a graph which shows a time-dependent change of the optimal melting temperature about the location corresponded to a corner part. It is a graph which shows the relationship between the spectral transmittance of glass, and a wavelength. It is a flowchart which shows one Embodiment of the silica glass crucible manufacturing method. It is a model front view which shows other one Embodiment of a silica glass crucible manufacturing apparatus. It is a graph which shows the change of the height position of the carbon electrode in one embodiment of the silica glass crucible manufacturing method concerning the present invention.

  Hereinafter, the silica glass crucible manufacturing method according to the present invention will be described in detail with reference to an embodiment of a silica glass crucible manufacturing apparatus suitably used for manufacturing.

FIG. 1 is a schematic front view showing an embodiment of a silica glass crucible manufacturing apparatus 1.
This silica glass crucible manufacturing apparatus 1 has a high output for heating and melting a silica powder layer 11 made of silica powder, which is a non-conductive object, by arc discharge with a plurality of carbon electrodes 13 in an output range of 300 kVA to 12,000 kVA. It is a device.

This silica glass crucible manufacturing apparatus 1 has a mold 10 as shown in FIG. The mold 10 is made of silica glass that can be rotated by a rotating portion (not shown) and has a substantially bowl-shaped inner surface shape made of carbon, and the inner surface shape of the bowl shape is similar to the crucible outer shape. It defines the outer shape of the crucible. A silica powder layer 11 made of silica powder is formed by supplying silica powder by spraying and depositing silica powder as a raw material powder to a predetermined thickness in the mold 10.
In addition, the mold 10 is provided with a plurality of decompression passages 12 which are opened on the inner surface thereof and connected to a decompression unit (not shown), and the inside of the silica powder layer 11 can be decompressed. A carbon electrode 13 connected to a power supply unit (not shown) is provided as an arc discharge unit at a position above the mold 10, and an arc flame is generated by the arc discharge of the carbon electrode 13, and silica powder of silica powder The layer 11 is heated and melted.

  The carbon electrode 13 is, for example, an electrode rod having the same shape so as to perform arc discharge of alternating current three phases (R phase, S phase, T phase), and has a vertex on the lower side as shown in FIGS. Each of the axes 13L is provided so as to form an angle θ1 (for example, 120 °) so as to form an inverted triangular pyramid. The number of electrodes, the arrangement state, and the power supply method are not limited to the above-described configuration, and other configurations can be employed.

  Further, the carbon electrode 13 can be moved up and down by the electrode position setting unit 20 as indicated by an arrow T in the figure, and from the height position of the electrode tip portion 13a (from the upper end position of the silica powder layer 11 (upper position of the mold opening)). The height position) H can be set. At the same time, the electrode opening of the carbon electrode 13 is variable by the electrode position setting unit 20, and the inter-electrode distance D and the like can be set as indicated by an arrow D in the figure. A relative position other than the height with the mold 10 can also be set.

Specifically, as shown in FIG. 1, the electrode position setting unit 20 supports the carbon electrode 13 so that the distance D between the electrodes can be set, and the support 21 can be moved in the horizontal direction. And a plurality of support portions 21 (that is, support portions of the respective carbon electrodes) and a vertical movement portion that allows the horizontal movement portions to be moved in the vertical direction.
In the support portion 21, the carbon electrode 13 is supported so as to be rotatable around the angle setting shaft 22, and has an electrode rotating portion that controls the rotation angle of the angle setting shaft 22.
In order to adjust the inter-electrode distance D of the carbon electrodes 13, the angle of the carbon electrode 13 is controlled by the electrode rotating part as shown by the arrow T3 in FIG. 1, and supported by the horizontal moving part as shown by the arrow T2. The horizontal position of the unit 21 is controlled. Further, the height position H can be controlled by controlling the height position of the support portion 21 by the vertical movement portion.
In addition, although the support part 21 etc. are shown only in the carbon electrode 13 of the left end in the figure, other electrodes are also supported by the same structure, and the height of each carbon electrode 13 can be individually controlled. Can do.

The carbon electrode 13 is formed of high-purity carbon particles having a particle diameter of 0.3 mm or less, preferably 0.1 mm or less, more preferably 0.05 mm or less, and the density thereof is 1.30 g / cm ³ to 1. 80 g / cm ^3, preferably when the ^{1.30g / cm 3 ~1.70g / cm 3} , it is possible to density differences carbon electrodes mutually arranged on the electrode of each phase is set to 0.2 g / cm ³ or less , Has high homogeneity.

  The silica glass crucible manufacturing apparatus 1 includes temperature measuring units (radiation thermometers Cam1, Cam2) that measure the actual temperature at a plurality of locations on the inner surface of the silica powder layer 11 that is heated and melted by the mold 10. Moreover, the silica glass crucible manufacturing apparatus 1 includes a temperature control unit that controls the actual temperature so that the actual temperature measured at the temperature measurement unit becomes the optimum melting temperature at each location that is input in advance. Yes.

Radiation thermometers Cam1 and Cam2 provided as a temperature measurement unit in the present embodiment measure the temperature by detecting radiant energy from a measurement target.
As shown in FIG. 1, the radiation thermometers Cam <b> 1 and Cam <b> 2 are disposed outside the partition wall SS that separates the inside and outside of the furnace that performs arc discharge. The radiation thermometers Cam1 and Cam2 obtain an optical system that collects radiant energy from the measurement target and a spectrum of light collected by the optical system through the filter F1 that covers the window provided in the partition wall SS. It has a spectroscopic unit and a detection element that detects light about the measurement target from the spectrum, and performs other predetermined signals such as an analog output of the detection element or a setting signal of the setting unit to perform a predetermined calculation. It is connected to a control unit for measuring temperature.

That is, each of the radiation thermometers Cam1 and Cam2 collects radiant energy light from the inner surface of the silica powder layer 11 through an optical system such as a lens, obtains a spectrum of the light by a spectroscopic unit, and obtains the spectrum from the spectrum. Light having a predetermined wavelength is detected by a detection element.
The analog output signal of the detection element is separated for each wavelength by a synchronous detector, amplified by an amplifier, and input to a control unit (CPU) via a multi-channel, low-resolution, small-bit AD converter to perform predetermined arithmetic processing. Thus, a desired temperature signal can be obtained. This temperature signal can be output to a display unit such as an LCD display, and is also output to the temperature control unit of the silica glass crucible manufacturing apparatus 1. And a temperature control part controls manufacturing conditions in real time from this information so that an actual temperature may meet the optimal melting temperature inputted beforehand.

  In this example, the radiation thermometer Cam1 measures the temperature of the inner surface of a portion (position RW) corresponding to the corner of the silica glass crucible in the silica powder layer 11, and the radiation thermometer Cam2 It is installed so as to measure the inner surface of the corresponding location (position W1).

  The temperature control unit is a means for controlling the actual temperature at each location by changing the heating and melting state of the silica powder layer 11, and is connected to the electrode position setting unit 20. The temperature control unit in this example varies at least one of the power supplied to the carbon electrode 13, the position state of the carbon electrode 13, the relative position state of the mold 10 and the carbon electrode 13, and the position state of the mold 10. Thus, the heating and melting state of the silica powder layer 11 is changed, and the actual temperature of each part is controlled.

Here, the position of the carbon electrode 13 refers to an electrode opening degree that is an angle formed by the plurality of electrodes, a horizontally separated state of the electrode tip portion 13a, or a separated state in the height direction of the electrode tip portion 13a, and a plurality of positions. The direction of the center direction of the electrode defined as the direction in which the arc flame formed by the carbon electrode 13 is ejected.
The relative position state between the mold 10 and the carbon electrode 13 refers to the relative positional relationship between the rotational axis direction of the mold 10 and the center direction of the carbon electrode 13, and the relative relationship between the mold 10 and the electrode tip 13a that can be regarded as an arc generation position. The height positional relationship (height) and the relative horizontal direction positional relationship (eccentricity, etc.) between the mold 10 and the electrode tip 13a that can be regarded as the arc generation position are included.
Further, the position state of the mold 10 includes the direction of the rotation axis of the mold 10 and the like.

Hereinafter, the manufacturing method of the silica glass crucible using this silica glass crucible manufacturing apparatus 1 is demonstrated.
First, the preliminary process which calculates | requires each optimal melting temperature previously about several places of the inner surface of the silica powder layer 11 in the mold 10 is performed.
Here, the optimum melting temperature is obtained empirically or by a calculation method such as simulation. For example, with respect to a large number of crucibles, the temperature behavior of a plurality of locations on the inner surface of the silica powder layer 11 over time during heating and melting at the time of manufacturing the crucible is measured by radiation thermometers Cam1 and Cam2. Get the data. On the other hand, the silicon crucible is pulled up at a high temperature of 1400 ° C. or higher by the CZ method using each of the many crucibles thus manufactured. And from the above temperature data about the crucible that was able to stably produce a silicon single crystal of good quality by the CZ method with good productivity, the optimum melting temperature over time at the time of heating and melting the silica powder layer 11 is determined empirically, or Determined by computational methods.

  If the optimum melting temperature is determined in advance for the temperature of the inner surface of each location, and the temperature of the inner surface is controlled in the subsequent temperature control process, the crucible's characteristics that greatly affect the characteristics of the silicon single crystal to be produced The state of the inner surface can be particularly suitably controlled.

Further, if at least one of the plurality of places has a corner portion, the melted state of the silica powder layer 11 can be controlled more precisely in the production of the silica glass crucible. For example, one of the plurality of places is in the corner and the other is in the wall.
As described above with reference to FIGS. 3 and 4, the corner portion is a portion located between the wall portion and the bottom portion, and is a portion where the temperature fluctuation during heating and melting of the silica powder layer 11 is large. However, this has been clarified by the study of the present inventor. For this reason, it is possible to further precisely control the state of the inner surface of the crucible and the like by obtaining an optimum melting temperature in advance for the corner portion and controlling the temperature of the portion so as to follow the optimum melting temperature.
Further, in the arc melting process, the portion near the boundary with the wall portion in the corner portion, in particular, the corner portion is a portion where the melted portion tends to hang down from the wall portion due to gravity, and the melted portion is caused by the centrifugal force of the mold 10 from the bottom portion. It is a part that tends to approach. Therefore, the corner portion is a portion where the thickness dimension tends to be larger than the set value. Therefore, by controlling the temperature so as to conform to the optimum melting temperature of the corner portion, it is also possible to particularly control the thickness dimension of the crucible.

FIG. 5 shows a method for manufacturing a silica glass crucible according to the present embodiment. Electric power supply is started at time t0 (S31 in FIG. 7) on the inner surface of the portion corresponding to the position RW, and power supply is performed at time t3. It is a graph which shows the optimal melting temperature with time at the time of stopping (S33 of FIG. 7).
In this graph, when a total of 10 crucibles (caliber: 914 mm, 36 inches) are manufactured, temperature data over time at the time of heating and melting at a position corresponding to the position RW are respectively obtained, and these temperature data are obtained. And the yield when the silicon single crystal was actually pulled up by the CZ method using the obtained crucibles and the yield of the final silicon wafer, etc. .

  The radiation thermometers Cam1 and Cam2 have a measurement temperature range of 400 to 2800 ° C., and preferably measure the temperature by detecting radiation energy having a wavelength of 4.8 to 5.2 μm. . When the measurement temperature range is 400 to 2800 ° C., the temperature at the time of heat melting of the silica powder layer 11 is covered. In the case of a temperature range lower than the above range, since the temperature has little influence on the crucible characteristics, there is not much meaning in measuring the temperature and obtaining the optimum melting temperature. On the other hand, a range higher than the above range may be set as the measurement range, but in reality, it is considered that the crucible is not manufactured at such a temperature.

In addition, if the temperature is measured by detecting radiant energy having a wavelength of 4.8 to 5.2 μm, a more accurate temperature can be measured. FIG. 6 is a graph showing the relationship between the spectral transmittance and the wavelength. As shown in this graph, the absorption band of CO ₂ that is considered to be generated from the carbon electrode 13 during arc discharge. Has a wavelength of 4.2 to 4.6 μm. Therefore, it is necessary to avoid this wavelength range in order to eliminate the influence on the temperature measurement due to the absorption of CO ₂ . Moreover, in order to measure the surface temperature of the silica glass which is a measuring object, it turns out that the transmittance | permeability of this silica glass needs to become 0, and a wavelength needs to be 4.8 micrometers or more. Further, the absorption band of H _{2 O} contained in the atmosphere to be an atmosphere of manufacturing a vitreous silica crucible, since the wavelength 5.2～7.8Myuemu, it is necessary to avoid this.
From these points, it is preferable to measure the temperature by detecting radiant energy of 4.8 to 5.2 μm.

The filter F1 is preferably made of BaF ₂ or CaF ₂ . Such a filter F has a high transmittance for light in the wavelength range emitted from the inner surface of the crucible. Therefore, the intensity of light used for temperature measurement is not reduced.
Further, the transmittance of the BaF ₂ or CaF _2, in order to decrease in the wavelength range of 8.0Myuemu～14myuemu, by not using the such a wavelength as measured wavelength can be measured more accurately temperature.

  At the time of temperature measurement, it is preferable that the observation line connecting the radiation thermometer and the measurement point is in a state separated from the carbon electrode by 100 mm or more. Thereby, the influence from the arc flame generated in the vicinity of the carbon electrode and the influence of the electrode radiation can be reduced and the accuracy of temperature measurement can be improved. Here, if the electrode is closer than the above range, the accuracy of temperature measurement is reduced, which is not preferable. If the electrode is separated from the carbon electrode 13 beyond the crucible radius, the set distance is larger than the crucible diameter. Therefore, the temperature at a predetermined measurement point cannot be measured, or the amount of radiation from the measurement point is reduced and the output of the radiation thermometer is insufficient, so that accurate temperature measurement tends to be impossible.

After performing the preliminary process as described above, the crucible is actually manufactured by the rotational molding method. FIG. 7 shows a flowchart of the manufacturing process.
Specifically, first, in the silica powder supply step S <b> 1, the silica powder layer 11 is formed by depositing silica powder on the inner surface of the mold 10. The silica powder layer 11 made of such quartz powder is held on the inner wall surface of the mold 10 by centrifugal force generated by the rotation of the mold 10.

  Next, in the electrode initial position setting step S2, as shown in FIGS. 1 and 2, the electrode position setting unit 20 maintains an inverted triangular pyramid shape such that the carbon electrode 13 has a vertex below, and The initial electrode position is set so that the axis 13L of the first electrode 13L contacts with each other at the tip 13a while maintaining the angle θ1. At the same time, the initial state of the mold-electrode relative position state consisting of the position and angle of the height position H and the electrode position central axis which is the central axis of the inverted triangular pyramid formed by the carbon electrode 13 and the rotation axis of the mold 10 Set.

Next, in the arc melting step S3, the position of the carbon electrode 13 is set, and the silica powder layer 11 is decompressed through the decompression passage 12 while being heated and melted in the arc discharge portion, thereby forming a silica glass layer. . The arc melting step S3 includes a power supply start step S31, an electrode position adjustment step S32, and a power supply end step S33.
In the power supply start step S31, power supply to the carbon electrode 13 is started as a power amount set as described above from a power supply unit (not shown). In this state, arc discharge does not occur.
In the electrode position adjusting step S32, the electrode position setting unit 20 maintains the inverted triangular pyramid shape such that the carbon electrode 13 has a vertex on the lower side or changes the angle to increase the inter-electrode distance D. Along with this, discharge begins to occur between the carbon electrodes 13. In this case, the power density of each carbon electrode 13 to control the power supplied by the power supply unit so that the ^{40kVA / cm 2 ~1,700kVA / cm 2} . Further, the mold position 10 and the carbon electrode 13 such as the height position H of the electrode are set so as to satisfy the conditions as a heat source necessary for melting the silica powder layer 11 while maintaining the angle θ1 by the electrode position setting unit 20. Sets the relative position state of. In this manner, the silica powder layer 11 is heated and melted.
In the power supply end step S33, after the melting of the silica powder layer 11 is in a predetermined state, the power supply by the power supply unit is stopped.
By this arc melting, the silica powder layer 11 can be heated and melted to produce a silica glass crucible.
In the arc melting step S3, the rotation state of the mold 10 is controlled by a control unit (not shown).

And in this embodiment, in such arc melting process S3, each of the inner surface of the location corresponding to the corner portion and the inner surface of the location corresponding to the wall portion is heated and melted by the radiation thermometers Cam1 and Cam2. A temperature measurement process that measures the actual temperature over time and a temperature control process that controls each actual temperature on the inner surface of these locations over time so as to obtain the optimum melting temperature obtained in the preliminary process. .
Specifically, based on the data of the optimum melting temperature and the actual temperature, the temperature control unit supplies power to the carbon electrode 13, the position state of the carbon electrode 13, the relative position state of the mold 10 and the carbon electrode 13, By varying at least one of the position states of the mold 10, the silica powder layer 11 is heated and melted while adjusting the actual temperature of each portion to the optimum melting temperature.
Thereby, about the silica powder layer 11 in a molten state, the inner surface of each location can be controlled to each optimal melting temperature in real time, and heating and melting can be performed while appropriately controlling the molten state of the silica powder layer 11. it can. As a result, a silica glass crucible whose crucible characteristics are appropriately controlled can be manufactured.

  Next, in the cooling step S4, the silica glass crucible after the power supply is stopped is cooled. Thereafter, the silica glass crucible is taken out from the mold 10 in the taking-out step S5. Then, as finishing process S6, the honing process which injects high pressure water to an outer peripheral surface, the rim cut process which makes a crucible height dimension into a predetermined state, and the washing process which wash | cleans the inner surface of a crucible with a hydrofluoric acid etc. are performed.

  In the present embodiment, the radiation thermometers Cam1 and Cam2 are positioned outside the partition wall SS of the arc furnace. However, as shown in FIG. 8, the radiation thermometers Cam1 and Cam2 may be housed inside the shield SS1 provided inside the partition wall SS. It is possible (illustration of the radiation thermometer Cam2 is omitted). In this case, the filter SS is provided on the shield SS1.

As described above, according to such a method for producing a silica glass crucible, the silica powder layer 11 in a molten state can be controlled in real time to the respective actual temperatures at a plurality of locations thereof, and therefore, The molten state of the silica powder layer 11 can be appropriately controlled. As a result, a silica glass crucible in which the crucible characteristics such as the state of the inner surface are appropriately controlled can be manufactured.
At that time, especially for the inner surface of the silica powder layer, the optimum melting temperature is obtained, and the actual temperature is measured and controlled, so that the state of the inner surface of the crucible that has a great influence on the characteristics of the silicon single crystal to be produced is particularly suitable. Can be controlled.
In the preliminary process, the optimum melting temperature is obtained over time, and in the temperature control process, the actual temperature is controlled over time, so that the crucible characteristics such as the state of the inner surface are more appropriately controlled. A silica glass crucible can be manufactured.
Furthermore, when at least one of the above-mentioned plurality of locations is a location corresponding to the corner portion of the silica glass crucible, the melting state of the silica powder layer can be controlled more precisely in the production of the silica glass crucible. .

  As the silica powder, synthetic silica powder can be mainly used corresponding to the inner surface layer, and natural silica powder can be used corresponding to the outer surface layer. Here, synthetic silica powder means what consists of synthetic silica. Synthetic silica is a chemically synthesized and manufactured raw material, and synthetic silica powder is amorphous. Since the raw material of the synthetic silica is a gas or a liquid, it can be easily purified, and the synthetic silica powder can have a higher purity than the natural silica powder. Synthetic silica materials are derived from gaseous materials such as silicon tetrachloride and liquid materials such as silicon alkoxide. In synthetic silica powder, it is possible to make all metal impurities 0.1 ppm or less.

Among the synthetic silica powders, silanol produced by hydrolysis of alkoxide usually remains in an amount of 50 to 100 ppm in the sol-gel method. Synthetic silica using silicon tetrachloride as a raw material can control silanol in a wide range of 0 to 1000 ppm, but usually contains about 100 ppm or more of chlorine. When alkoxide is used as a raw material, synthetic silica containing no chlorine can be easily obtained.
The synthetic silica powder by the sol-gel method contains about 50 to 100 ppm of silanol before melting as described above. When this is melted in a vacuum, silanol desorption occurs, and the silanol of the silica glass obtained is reduced to about 5 to 30 ppm. The amount of silanol varies depending on the melting conditions such as the melting temperature and the temperature rise. Under the same conditions, the silanol content of natural silica glass is less than 5 ppm.

In general, synthetic silica glass is said to have a lower viscosity at higher temperatures than natural silica glass. One reason for this is that silanol or halogen cuts the network structure of the SiO ₄ tetrahedron.
Synthetic silica glass is considered to have characteristics close to those of synthetic silica glass using silicon tetrachloride as a raw material, which transmits ultraviolet rays up to a wavelength of about 200 nm and is used for ultraviolet optical applications, when the light transmittance is measured.
In synthetic silica glass, when a fluorescence spectrum obtained by excitation with ultraviolet light having a wavelength of 245 nm is measured, a fluorescence peak as in natural silica glass is not observed.

Natural silica powder means a powder made of natural silica. Natural silica is a raw material obtained by digging up raw quartz ores that exist in nature, crushing and refining, and natural silica powder is α- Made of quartz crystals. Natural silica powder contains 1 ppm or more of Al and Ti. In addition, metal impurities are at a higher level than synthetic silica powder. Natural silica powder contains almost no silanol. The amount of silanol in natural silica glass is <50 ppm.
In natural silica glass, when the light transmittance is measured, the transmittance is drastically reduced when the wavelength is 250 nm or less due to Ti contained mainly as an impurity at about 1 ppm, and hardly transmits at a wavelength of 200 nm. In addition, an absorption peak due to an oxygen deficiency defect is observed near 245 nm.

In natural silica glass, when a fluorescence spectrum obtained by excitation with ultraviolet light having a wavelength of 245 nm is measured, fluorescence peaks are observed at 280 nm and 390 nm. These fluorescence peaks are due to oxygen deficiency defects in the glass.
Whether the glass material was natural silica by measuring the concentration of impurities contained, measuring the difference in the amount of silanol, or measuring the light transmittance, or measuring the fluorescence spectrum obtained by excitation with ultraviolet light having a wavelength of 245 nm. Whether it was silica or not can be determined.

  In the present invention, silica powder is used as the raw material powder, but the silica powder may be synthetic silica powder or natural silica powder. The natural silica powder may be a quartz powder, or may be a powder of a material known as a raw material for a silica glass crucible such as quartz or silica sand. Further, the silica powder may be in a crystalline state, an amorphous state, or a glass state.

  As mentioned above, although embodiment of this invention was described, these are illustrations of this invention and various structures other than the above are also employable. Moreover, it is also possible to adopt a combination of the configurations described in the above embodiments.

  As an example of the present invention, ten crucibles having a diameter of 610 mm (24 inches) were manufactured and designated as Experimental Example A. At this time, the electrode position setting unit 20 shown in FIG. 1 sets the height position H of the electrode tip 13a by changing the reference position with time as shown in FIG. The height position H1 was set from time t0 to t1, the height position H2 was set from time t2 to t3, and the respective height positions were set to satisfy H1> H2.

At the same time, the temperature during the arc melting is measured at the position RW shown in FIG. 3, and the measured temperature is set to the optimum melting temperature (set temperature) preset as shown in FIG. 5 for the position RW. The height position H was adjusted and the supplied power was finely adjusted so as to be within an allowable range of ± 15 ° C. Similarly, at the position R, fine adjustment by the measurement temperature was performed.
Furthermore, ten crucibles were manufactured under the same conditions as described above and without temperature measurement and fine adjustment only by setting the height position, and were used as Experimental Example B.
In the silica glass crucible thus manufactured, the thickness dimension was measured at the corner corresponding to the position R.
As a result, in Experimental Example A, the corner portion thickness dimension corresponding to position R did not deviate from the specified value of 12 mm ± 0.5 mm, whereas in Experimental Example B, 12.6 mm was obtained. One, 12.8 mm, 1 13 mm, and 3 crucibles having values larger than the standard were obtained.
From this result, it can be seen that the variation in the thickness that seems to be caused by the non-uniformity of the temperature control can be suppressed by performing temperature measurement and fine adjustment at a plurality of locations as in Experiment A.

  In the above, this invention was demonstrated based on the Example. It is to be understood by those skilled in the art that this embodiment is merely an example, and that various modifications are possible and that such modifications are within the scope of the present invention.

1. Silica glass crucible manufacturing equipment,
DESCRIPTION OF SYMBOLS 10 ... Mold 11 ... Silica powder layer 12 ... Pressure-reduction channel | path 13 ... Carbon electrode 13a ... Electrode tip part 13L ... Axis 20 ... Electrode position setting part 21 ... Support part 22 ... Angle setting axis Cam1, Cam2 ... Radiation thermometer SS ... Bulkhead F1 ... Filter SS1 ... Shield

Claims (4)

In a rotating mold, a silica powder layer is heated and melted by arc discharge with a plurality of carbon electrodes to produce a silica glass crucible,
For a plurality of places where the height position of the silica powder layer is different, a preliminary step for obtaining in advance the optimum melting temperature at the time of heating and melting,
A temperature measuring step for measuring an actual temperature at the time of heating and melting at the plurality of locations;
And a temperature control step of controlling the actual temperatures at the plurality of locations so as to achieve the optimum melting temperature.   The method for producing a silica glass crucible according to claim 1, wherein the optimum melting temperature and the actual temperature are temperatures of the inner surfaces of the plurality of locations.   The method for producing a silica glass crucible according to claim 1 or 2, wherein the optimum melting temperature is obtained over time, and the actual temperature is controlled over time.   The method for producing a silica glass crucible according to any one of claims 1 to 3, wherein at least one of the plurality of places is a place corresponding to a corner portion of the silica glass crucible.